The present invention relates to an electrode system for a resistance heating furnace.
In resistive furnaces which employ conductive crucibles for the combustion of a specimen for subsequent analysis by an analytical instrument, during the heating of the combustion of the specimen at temperatures in the neighborhood of 2500.degree. C or even higher the electrodes between which the resistive crucible is clamped become contaminated by the byproducts of combustion. Thus it is necessary after at least the running of a few specimens to clean the electrode surfaces, including the interior cavity of the electrodes into which the crucible is fitted. In the past, known electrode systems have been of a two-piece construction with one of the electrodes defining a cavity into which the crucible extends. Such construction is represented by U.S. Pat. No. 3,936,587 issued on Feb. 3, 1976, to Sitek et al. and assigned to the present assignee. Such electrode construction, although performing well, requires frequent cleaning typically with a special cleaning brush or the like which must be extended into the electrodes for their cleaning.
Further with the prior at electrode construction, although the lower electrodes included a pedestal for centering the crucible thereon before the electrodes are brought together clamping the crucible therebetween; on some occasions the crucible does not center properly. As a result when the crucible is clamped between the electrodes, it may be crushed, or poor electrical contact is made between the electrode and the upper rim of the typically cylindrical crucible. This, of course, reduces the resistance heating of the crucible due to a reduction in electrical current through the crucible.